The present invention relates generally to the field of microstrip antennas, and more particularly to planar tunable microstrip antennas for the HF and VHF frequencies.
Microstrip antennas with a lightweight, low profile, low cost and planar structure have been replacing bulky antennas. The length of a rectangular microstrip antenna is about a half wavelength within the dielectric medium under the radiating patch, which is still relatively large at UHF and VHF frequencies, but these frequencies can impose size limitations resulting in bulky and cumbersome antenna structures. Due to the size limitation at UHF and VHF frequencies, previously available microstrip antennas were mainly limited to applications at higher frequencies. The disadvantage of size limitations in UHF and VHF has created a long-felt need to reduce antenna length. Up until now, it has not been possible to employ planar microstrip antennas without the disadvantages, limitations and shortcomings associated with antenna length and size. The present invention makes it possible to fulfill the need for an electrically small planar tunable microstrip antenna for the HF and VHF frequencies.
The long-awaited electrically small planar tunable microstrip antenna at for the HF and VHF frequencies offers a number of advantages over prior art antennas. Prior art rectangular microstrip antennas have a half wavelength length within the dielectric medium under the radiating patch, and this is extremely large at UHF and VHF frequencies. The electrically small planar microstrip antenna of the present invention provides the same high efficiency as conventional microstrip antennas, but it also offers a number of key advantages that permit significant decreases in antenna size, without suffering from the size limitations of prior art antenna structures. The present invention also fulfills the long-felt and unsatisfied need for an electrically small antenna for the lower frequencies.
The present invention fulfills the long-standing need for a significantly reduced antenna length and an electrically small antenna for the lower frequencies with a microstrip antenna structure fabricated with ferrite and ferrite-ferroelectric composite materials that permit both a considerably reduced antenna length and significantly high efficiency antenna performance. This invention""s electrically small planar microstrip antenna also provides the additional advantage of being tunable. The present invention also advantageously provides an antenna with the same high efficiency as quarter wavelength monopole and conventional microstrip antennas, but with an antenna length shortened to about 1% of the length of a monopole antenna or conventional microstrip antenna, resulting in small microstrip antennas at low frequencies such as HF and VHF without suffering from the disadvantages, shortcomings and limitations of prior art microstrip antennas. To compensate for their very narrow bandwidth, these antennas can be easily tuned.
It is an object of this invention to provide an electrically small planar tunable microstrip antenna.
It is another object of this invention to provide an electrically small planar tunable microstrip antenna composed of ferrite materials that permits a substantial reduction in antenna size.
It is yet another object of this invention to provide an electrically small planar tunable microstrip antenna composed of ferrite materials that permits a substantial reduction in antenna size and operates efficiently at low HF and VHF frequencies.
It is still another object of this invention to provide an electrically small planar tunable microstrip antenna composed of ferrite-ferroelectric composite materials that permits a substantial reduction in antenna size and operates efficiently at low HF and VHF frequencies.
These and other objects are advantageously accomplished with the present invention providing an electrically small planar tunable microstrip antenna comprising stacking a radiating element, a ferrite microstrip dielectric substrate and a ground plane coupled to a means for tuning to provide an electrically small, compact, planar tunable microstrip antenna at HF and VHF frequencies. The present invention also provides an electrically small planar tunable microstrip antenna using ferrite-ferroelectric composite materials for the microstrip dielectric substrate. In the ferrite-ferroelectric embodiment, the present invention provides an antenna length that is substantially shortened to approximately 1% of the length of a monopole antenna or conventional microstrip antenna with tuning accomplished by a multi-turn coil mechanism. This invention also encompasses methods for providing substantial reduction in antenna size at the HF and VHF frequencies with electrically small planar tunable microstrip antennas comprising a dielectric substrate composed of ferrite and ferrite-ferroelectric composite-materials.